Put ScalaTags and ScalaDom in the 'Selected' libraries by default

[zarthross]

It appears as if scalatags and scaladom are included by default, but there isn't any indication in the UI. It would be nice if they were just added to the 'Selected' section by default. If it its not possible to remove them as a dependency, can we just show them under 'Selected' but not allow them to be removed?

[ochrons]

This is how it was at some point but I removed it to keep the UI simpler. The Fiddle helper depends on these libs, so the correct action would be to make the helper optional.

[zarthross]

I'm fine with the idea of the Fiddle helper library being optional, as long as Scala-Tags and Scala-Dom get added to the 'Available' list to help reduce confusion.